depends on your needs.
compared to the GT-8, the XT Live is a more accessible recording machine (thanks to USB support and the Gearbox software). the XT Live also has a better pallette of amp and cabinet simulations and it might still continue to grow as Line 6 continues to support the device with different sorts of upgrades. but if you want better control of effects and the signal chain, the GT-8 is the way to go. it can be a tweaker's dream.
people are free to contest. but the way i see it, the XT Live is an amp and cab sim platform that happens to have other effects and geared very much towards USB recording. while the GT-8 is skewed more towards being a true effects platform.